Production of magnesium



Patented July 31, 1945 PRODUCTION or MAGNESIUM Roy 0. Kirk, Midland, Mich, asslgnor to The Dow Chemical Company, Midland, Mich, a corporation of Michigan No Drawing. Application May 2, 1942, Serial No. 441,535

.sium oxide be used in order to maintain the per- 6 Claims.

This invention concerns an improved method or preparing magnesium by the thermal reduction or magnesium oxide, using carbon as the reducing agent.

It is known that magnesium can be prepared by heating a mixture of magnesium oxide or a magnesium oxide-containing material with carbon whereby magnesium is liberated as a vapor,

which may be withdrawn and condensed. How-' ever, in commercial operations using impure magnesium oxide, difllculty has been experienced in the removal of the residue --o t,thisreaction from the reduction furnace, said residue consist- I ing usually or compounds calcium and silicon in the form of complex silicates. Normally the residue remaining is a sintered or a very hard solid and is removed only with dlfllculty. Such obvious and simple methods of removal as the use of screw conveyors cannot be used because I of. the size and hardness of the pieces to be removed. I

It.is', therefore, desirable to produce a solid residue which is powderedor easily powderable so that it can be conveniently removed irom the furnace. It is the principal object or this invention to provide a method for the production of magnesium by the reduction or impure magnethe range indicated above.

slum oxide which will produce such a powdered I residue.

I have now found that a powdered residue can be obtained in the reduction 01 magnesium oxide with carbon by a process which comprises forming a charge consisting essentially of magnesium oxide, carbon in a proportion at least chemically equivalent thereto, lime, silica, and alumina, the

lime, silica, and alumina being present in such proportions that the residueiormed on reduction amounts to less than about 20 per cent or the total charge and has the composition:

and carrying-out the reduction at a temperature below the iusion temperature or the residue.

Although the invention contemplates the broad range or proportions listed above, a preierred Per cent by weight -Ca 52 to 98.8

810: I 0.1 to 48 AlrO 0.1-to 80 centage or residueas low as possib e and less than about 20 per cent. For example, calcined dolomite cannot be used except where it is present in a minor proportion. in an ore relatively richer in magnesia. Ordinarily the magnesium oxide is added as calcined magnesite. The car- I bon is ordinarily added as graphite, carbon blacir, coke, coal, etc. The hme, silica, and alumma.may be present in pure form, as ores or these materials, or in comomed form as in sillcates and aluminates. 1t irequently occurs that the magnesium oxide from which the magnesium is to be liberated contains significant proportions or lime, silica,.or alumina. It is necessary, therei'ore, to determine'these proportions by chemical anawsis and then adjust the charge to provide a residue having compositional proportions within In many cases other constituents such as iron oxide will be found in the magnesia ore, but these additional ingredients are usually not present in a proportion sumcient to alter significantly the properties or the residue.

. The residue should not exceed about 20 per cent of the charge in order to avoid hardening of the solid residue. That the hardening can be avoided by so restricting the proportion 01 residue is believed due to the fact that where a small proportion of residue is used, the particles 0! the inert material are far apart during most or the reaction time and havelittle opportunity to cling together. Where a large proportion of inert materials is used, however, the particles or said material are close together over a large traction of the time they are exposed to the high temperature ot the reduction furnace, and thereby have the opportunity to harden into a solid mass or at least intoa difiicultly powderable mass. .Thus,

the present invention depends on both a regulation 01' the proportions of the residual ingredients with respect to each other and a regulation oithe proportion 01 the residue withrespect to the total charge.

The temperature at which the reduction is best carried out is determined principally by the pressure in the reduction furnace and may vary irom about 1400 C. at extremely low pressures to about 2100' C. at atmospheric pressure. However, tor any particular temperature 0! operae tion, the proportions o1 lime, silica, and alumina can be adjusted within the reuse. indicated to produce a residue having a rusion temperature higher than the temperature oi" operation and.

It'umerred thatareasonablypuremagneg accordingly, to produce a powdered m my powderabie residue. The fusion temperatures of the residues included within the-scope of the present invention vary from about 1500 0. up-

ward, and can be determined for any. specific compositions from the well-known CaO-SiOa- A110: ternarydiagram, e. g. as reproduced in Jour. Amer. Ceram. Soc. 6, 524 (1933).

' In practice the magnesium oxide, carbon, and such'of the oxides, lime, silica. and alumina,-asare not present in the magnesium oxide-containing material in suitable proportions are mixedas hereinbefore explained and ground to a fine powder. In order toav'oid blowing the powdered charge into the magnesium condensing system during reduction the mixture may, if

20 per cent of the total charge and has the composition:

' Per cent by weight CaO 52 to 98.8 SiO: 0.1 to 48 Y AlaO: 0.1 to 30 desired, he formed into briquettes with the aid of a tar binder, or other carbonaceous binder, and baked. Thecharge in the form of briquettes is then introduced into the reduction furnace. and heated to a suitable temperature below the fusion' temperature .of the CaOSiO:-Alz= residueunder nonoxidizing conditions, i. e. under reduced 1 pressure or in the presence of an inert'gas such I as hydrogen orhelium. At the operating temperatures magnesium is liberated as a vapor, which may be withdrawn and condensed to recover the metal. The powdered or easily powsilica, and alumina in such proportions that the residue formed on reduction amounts to less than Per cent by weight 'CaO 55 to 98.8 810: 0.1 to A190 0.1 to 30 and heatihg the charge at a reduction temperaturebelow the fusion temperature of the residue to liberate magnesium as a vapor.

derable residue, consisting essentially of lime;

silica. and alumina, may be easily removed from the furnace by means of a screw conveyor;

'I claim:

1. In a process for the production of magne- 1 slum. the steps of forming a charge consisting essentially of magnesium oxide, carbon in a proportion at least chemically equivalent thereto. and the oxides lime, silica, and alumina in such proportions that the residue formed on reduction amounts to less than per cent ofthe total charge and has the composition:

and heating the charge at a reduction temperature below the fusion temperature of the residueto liberate magnesium as a vapor.

.2. In a process for the production of magneslum. the steps of forming a charge consisting essentially of magnesium oxide, carbon in a pronto liberate magnesium-as a vapor.

portion at least chemically equivalent thereto, and the oxides lime. silica, and alumina in such proportions that the residue formed on'reduction amounts to less than 20 per cent of the'total charge and has the composition:

Per cent by weight j to 98.8

0.1 to 15 AhOa 0.-1 to and heating the charge at a reduction temperature below thefusibntemperature of the residue 3. ma process for the reduction of magnesium oxide with carbon in a proportion at least chemieally equivalent thereto, the steps of adjusting the composition of the charge to contain lime,

5. In a process for the production of magneslum the steps of forming a powdered charge consisting essentially of magnesium oxide, carbon in a proportion at least chemically equivalent thereto, an the oxides lime, silica, and alumina in such pr rtions that the residue formed on reduction amounts to less than 20 per cent of the 35 total charge and has the composition:

a u Per cent by weight 1 CaO 52 to 98.8 Si 0.1 to 48 m A: 0.1 to 30 mixing the powdered charge with'a carbonaceous binder; briquetting the mixture; and heating the briquettes-at a reduction temperature below the fusion temperature of the residue to liberate magnesium as a vapor.

6. In a process for slum by the reduction of magnesia with carbon wherein the magnesia employed contains as im- Purity a small proportion of at least one of-the oxides lime, silica, and alumina, the method of insuring retention of the said impurities in the reduction zone in the form of a powdered residue which comprises adding such otherof the oxides lime, silica, and alumina to the reduction charge in proportions relative to that of the impurity as 'to insure that the total residue to be formed represents less than 20 per cent by-weight-of the charge, has a fusion temperature above the reduction temperature to ho employed, and has a composition falling within the limits Per cent by weight Ca 52 to 98.8 SiQ 0.1 to 48 A120: 0.1 to 30 no? 6. ms.

the production of magne- I 

